Travelling wave tube having improved efficiency

ABSTRACT

The efficiency of a travelling wave tube is improved by the provision of a resonance section having a decreased delay interval with regard to the normal delay interval of the delay line of the tube. The resonance section is interposed in the delay line at the collector-side end of the delay line in such a manner that reflecting impact points are present at its ends and that at a medium operational frequency of lambda o the length of the resonance section is 1 n lambda L/2.

United States Patent Heynisch I [451 July 18, 1972 [54] TRAVELLING WAVE TUBE HAVING IMPROVED EFFICIENCY [21 Appl. No.: 94,323

[30] Foreign Application Priority Data Dec. 23, 1969 Germany ..P 19 64 721.3

[52] US. Cl ..3l5/3.6, 315/393 [51] Int. Cl. ..H0lj 25/34 [58] Field ofSearch v.3l5/3.5, 36, 39.3

[56] References Cited UNITED STATES PATENTS 2,922,920 1/1960 Convert ..3l5/3.6

ELgLCJIIlIIRON 5 2,580,007 12/1951 Dohler et al. ..3 I 5/3.5 3,020,439 2/1962 Eichenbaum ..3 l 5/3.6 3,292,033 12/1966 Kenmoku ...3l5/3.6 3,391,299 7/1968 Bodmer et al. ..3 l 5/3.6

Primary Examinen-Herman Karl Saalbach Assistant Examiner-Saxfield Chatmon, Jr. Attorney-Hill, Sherman, Meroni, Gross & Simpson [57] ABSTRACT The efficiency of a travelling wave tube is improved by the provision of a resonance section having a decreased delay interval with regard to the normal delay interval of the delay'line of the tube. The resonance section is interposed in the delay line at the collector-side end of the delay line in such a manner that reflecting impact points are present at its ends and that at a medium operational frequency of A, the length of the resonance section is l =n)\,j2.

8 Claim, 1 Drawing Figure COLLECTOR 2 PATENTED JUL 1 8 I972 IN VENTOR l /l flP/Cb Hey/Nisan ATTYS.

W W I TRAVELLING WAVE TUBE HAVING IMPROVED EFFICIENCY BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a traveling wave tube with a delay line which is interposed between an electron beam producing system and an electron beam collector, which delay line contains sections having different degrees of delay.

2. Description of the Prior Art The delay mechanisms of travelling wave tubes require a certain relationship between the speed of the electrons of the electron beam and the electromagnetic wave to be amplified which is carried on the delay line, whereby the electron beam speed must be somewhat larger than the axialspeed of propagation of the wave. Therefore, merely a small portion of the energy of the electron beam can be applied for amplification of the electromagnetic wave with a line having constant parameters since the loss of speed of the electronbeam which occurs during amplification of the wave interrupts the travelling field amplification mechanism.

In the prior art the conversion efficiency of travelling wave tubes can be improved by means of adapting the wave speed to the electron speed at that portion of the delay line which is at the outlet side. The speed tapering" can thereby beeffected by means of a change of the line parameters, particularly by means of decreasing its period, either in stages or according to a continuous function.

Another possibility to improve the conversion efficiency due to a subsequent correction of the relationship of axial speed of the electromagnetic wave to the speed of the electron beam resides in adapting the electron speed to the unchanged wave speed by means of a single stage or multi-stage speed changes. However, the delay line must then be interrupted galvanically to subsequently speed up the beam, which technique leads to essential difficulties with respect to further impactfree guidance ofthe wave.

SUMMARY OF THE INVENTION This invention therefore has as its primary objective to provide furtherimprovements in the increase of'conversion efficiency which can be obtained by means of tapering the wave speed, i.e. by means of a change of the parameters of the delay line at that end of the travel wave tube which is adjacent the output.

To realize the foregoing objective, it is herewith proposed for a travelling wave tube of the kind mentioned above, according to this invention, that a section (resonance section) with a increased delay interval with regard to the normal delay interval the delay line, be inserted at the collector-side end of the delay line that way a reflecting impact points are present at its demarkations and that, at a medium operational frequency the length of the resonance section is expressed as l nA /2 L=wave length of the medium operational frequency A, on the line.

The delay interval in the resonance section may thereby be staged several times and/or continuously according to any given function, however, that delay interval and the resonance section willbe kept generally constant in order to avoid,making the construction of the line any more complicated than necessary.

The present invention therefore proceeds from the discovery that it suffices for most uses of travelling wave tubes, even if the fact is taken into account that one of itsmain advantages is being broad-banded, if the transmission band width is about -20 percent. With travelling wave tubes designed in accordance with this invention, that portion of the band width which exceeds further than this trans-mission band width can be applied for the increase of conversion efficiency via a resonance-rise effect. The decrease of the band width which is necessarily connected with the resonance rise, thus, according to the foregoing statements, does not constitute any impairment of the transmission condition in most cases, since the possible band width in many cases is never completely utilized.

It is also provided in a further development of the present invention that the end section of the delay line which follows the resonance sections is designed as a single or multi-staged M4 transformer in a way that practically no interaction occurs with the electron beam along its length.

The delay line is to be measured in a manner that the microsignal amplification in the section between the damping section arranged at the beam producing input of the delay line at the resonance section is larger than 25 dB.

BRIEF DESCRIPTION OF THE DRAWING Other objects, features and advantages of the invention, its organization, construction and operation will be best understood from the following detailed description of a preferred embodiment of the invention taken in conjunction with the accompanying drawing which carries a single FIGURE that schematically illustrates a travelling wave tube. Parts of the apparatus which are not essential for the understanding of this invention such as the vacuum shell of the tube and the magnet system for the bundled guidance of the electron beam have therefore been left out of the figure for clarity.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 schematically illustrates the construction of a travelling wave tube having a spiral delay line. The electron beam is produced in the usual manner with an electron gun I and guided through the spiral chamber to a collector 4 with the aid of a homogeneous field (permanent magnet field; coil field) or a periodic permanent magnet field. The high frequency signal HF to beamplified is coupled into the input-side portion of the spiral line 6 by way of an input line 2 and there amplified in the usual manner. Beginning in this portion of the tube must be larger than the so-called distribution damping so that the electron beam obtains its complete modulation and can stimulate the output-side part 7 of the spiral. Both spiral portions are decoupled as well known in the art by means of a practically reflection free damping zone 5. The output-side spiral 7 and the coils 8 and 9 are designed in a very distinct manner to obtain a particularly great efficiency. Proceeding from the damping zone 5 which must be arranged as near as possible to the input 2 of the spiral (for large N and small phase distortion), there is first of all a spiral section with an even delay. For this section, the condition is valid that the micro-signal or micro wave amplification must be at least 25 dB in order to reach the maximum efficiency. Next there is a spiral section 8 which is closed off by two reflection points. The reflection factor r or r can have any values (most often however r will be r In this manner, the spiral section 8 has an effect like a line resonator. lts length is thus tuned to the desired operational frequency (l nA /Z). The resonance .rise, i.e. the factor of merit Q is determined with the size of the reflector factors r,, r The effective band width will therefore result. After the spiral section 8 there is connected a spiral section 9 which is designed as a single stage or as a multi-stage l4 transformer in a way that it does not allow practically any interaction with the electron beam. Finally, the amplified wave is extended to the consumer by way of a decoupling line 3 in which a circulator 10 is interposed.

By means of the resonance rise in the spiral section 8, it is provided that the E fields for the interaction with the electron beam become sufficiently large that the efficiency is essentially increased by means of the extreme braking action of the electrons. In order to optimize this effect, it is necessary to adapt the delay of the spiral section 8 to the adjusted factor of merit Q in away that the maximum braking action of the electrons is possible. Therefore, the delay in the spiral section 8 is dimensioned as follows:

a. larger c/v than in the spiral section 7 and even over the length of the section 8.

min/1s nnla b. larger c/v values than in section 7, however, stages several times.

c. larger c/v values than in section 7, however, extending continuously according to any certain given function.

c. lnterchangingly larger and smaller c/v values, staged or continuous.

These changes of the c/v values can be obtained by means of diameter changes of the spirals, increase changes of the spirals or by means of approximation of metallic or dielectric coatings ofthe spiral according to predetermined functions.

A change of the ya-value can also be applied.

Herewith a given course of the amplification curve (dependent on frequency) can also be realized if the ya values of the spiral sections 6, 7 and 8 are selected to be different.

A further measure for the improvement of efficiency is an increase of the magnetic guidance field for the electron beam in the spiral section 8. Here the magnetic field must be adapted to the degree of strong interaction, i.e. the beam braking action. Therefore, a magnetic field increase according to a given function is necessary which depends on the resonance rise in the spiral section 8.

It should be finally pointed out that the entire operational efficiency, even with the above described arrangement, can be still further improved by also applying prior art techniques including the use ofa brakage collector.

Many changes and modifications may become apparent to those skilled in the art without departing from the spirit and scope of the invention, and it is to be understood that I intend to include within the patent warranted hereon all such changes and modifications as may reasonably and properly be included within the scope of my contribution to the art.

What I claim is:

l. A travelling wave tube comprising an electron beam producing system, an electron beam collector and a delay line operatively connected between said electron beam generating system and said electron beam collector, and wherein said tube further comprises a resonance section interposed in said delay line and having a increased delay time with respect to the normal delay of the delay line, said resonance section interposed adjacent said electron beam collector to effect reflection points at its ends, and wherein at the medium operational frequency A the length l of the resonance section is defined by the expression 1 nA /2, where n is a stage integer and is the wave length of a wave at the frequency A,,.

2. The travelling wave tube of claim 1, wherein the delay interval of said resonance section is constant.

3. The travelling wave tube of claim 1, wherein reflection factors are established at said reflection points and said resonance section is constructed to provide equal reflection factors at each end thereof.

4. The travelling wave tube of claim 1, wherein said resonance section is interposed to provide a portion of said delay line between said resonance section and said collector as a M4 transformer whereat there is no interference with the electron beam.

5. The travelling wave tube of claim 4, wherein said M4 transformer is a single stage device.

6. The travelling wave tube of claim 4, wherein said M4 transformer is a multi-stage device.

7. The travelling wave tube of claim 1, wherein said delay line includes an input damping section and wherein said delay line provides microsignal amplification of greater than 25 dB between said damping section and said resonance section.

8. The travelling wave tube of claim 1, comprising means for providing a greater magnetic field to said resonance section than to the remainder of said delay line to effect a beam braking action. 

1. A travelling wave tube comprising an electron beam producing system, an electron beam collector and a delay line operatively connected between said electron beam generating system and said electron beam collector, and wherein said tube further comprises a resonance section interposed in said delay line and having a increased delay time with respect to the normal delay of the delay line, said resonance section interposed adjacent said electron beam collector to effect reflection points at its ends, and wherein at the medium operational frequency lambda o the length 1 of the resonance section is defined by the expression 1 n lambda L/2, where n is a stage integer and lambda L is the wave length of a wave at the frequency lambda o.
 2. The travelling wave tube of claim 1, wherein the delay interval of said resonance section is constant.
 3. The travelling wave tube of claim 1, wherein refleCtion factors are established at said reflection points and said resonance section is constructed to provide equal reflection factors at each end thereof.
 4. The travelling wave tube of claim 1, wherein said resonance section is interposed to provide a portion of said delay line between said resonance section and said collector as a lambda /4 transformer whereat there is no interference with the electron beam.
 5. The travelling wave tube of claim 4, wherein said lambda /4 transformer is a single stage device.
 6. The travelling wave tube of claim 4, wherein said lambda /4 transformer is a multi-stage device.
 7. The travelling wave tube of claim 1, wherein said delay line includes an input damping section and wherein said delay line provides microsignal amplification of greater than 25 dB between said damping section and said resonance section.
 8. The travelling wave tube of claim 1, comprising means for providing a greater magnetic field to said resonance section than to the remainder of said delay line to effect a beam braking action. 